   "Returns true if x is the value true, false otherwise."
   [x] (cljs.core/true? x))
 
-(defn ^boolean undefined? [x]
+(defn ^boolean undefined?
+  "Returns true if x identical to the JavaScript undefined value."
+  [x]
   (cljs.core/undefined? x))
 
 (defn ^boolean seq?

           a)))))

(defn object-array
  ([size-or-seq]
     (if (number? size-or-seq)
       (object-array size-or-seq nil)

           a)))))

(defn double-array
  "Creates an array of doubles. Does not coerce array, provided for compatibility
  with Clojure."
  ([size-or-seq]
     (if (number? size-or-seq)
       (double-array size-or-seq nil)
